Breath testing has been used in medicine since ancient times.
There have been considerable improvements in tests which can be applied to breath samples for diagnostic purposes. These improvements have prompted renewed efforts to develop breath sample collection devices and methods. A breath sample collection device must meet several conflicting requirements. To avoid the possible infection risks associated with reusable devices, the sample collection device should be disposable. Therefore, the device should be manufacturable at low cost. However, the device should provide for secure capture of a breath sample which truly represents the content of the breath stream at, a particular time during exhalation. The air expelled by a patient during exhalation varies in composition. The first air expelled consists essentially of air disposed in the mouth, nose and upper respiratory tract. Air expelled at a later time during the same exhalation will consist essentially of air from the bronchi and lower respiratory tract, whereas the last air expelled will consist essentially of air from the alveolar or air sacks of the lungs themselves. It is desirable to capture a particular portion of the exhaled air to provide a test sample which truly represents one portion, and one portion only, of the breath. For example, in metabolic testing it is generally desirable to capture alveolar air, and to exclude other portions of the exhaled air. Thus, the sampling device should be capable of selectively capturing a desired portion of the breath stream without substantial contamination by other portions of the breath stream. The device must also provide for secure storage of the captured sample until the same can be transferred to an analytical instrument. The device should be simple to use, both in capturing the sample and in transferring the sample to an analytical instrument. All of these requirements, taken together, have posed considerable technical challenge heretofore.
One device which has been proposed uses a plastic bag with attached mouthpiece into which the patient expels an expired breath stream. While the expired breath is still being expelled, a syringe is used to draw off a sample. Once the sample is collected, a stopcock on the syringe is closed and a needle is affixed to the end of the syringe. A portion of the sample is then placed in a test tube by using the needle to pierce the sealing membrane of an evacuated test tube. The sample captured in the bag will be a mixture of all portions of the exhaled breath, including air present in the lungs, respiratory tract and the mouth. The sample therefore will not accurately represent any particular portion of the exhaled breath. Another device using a flexible bag is described in U.S. Pat. No. 5,140,993, and suffers from similar drawbacks.
Another device uses a test tube-like sample container which has a permanently closed bottom end and an open top end or mouth. A membrane with two crossed slits is fixed at the mouth of the container.
The user inserts a straw through the cross-slits of the membrane, so that an open end of the straw is disposed adjacent to the bottom end of the container. The user then blows through the straw, forcing breath through the container and out of the mouth of the container by way of the slits in the membrane. To terminate the sample, the user must pull the straw out of the container. It is not possible to seal out extraneous air from outside the container during the test. The straw does not provide for complete purging of the container. There is some mixing of the breath entering with the air in the container. While the straw is being withdrawn, the air at the bottom of the container remains undisturbed. Thus, the sample left in the container will be contaminated with air from undesired parts of the exhalation cycle. Also, as the straw is withdrawn so that the sealing cap can be applied, there is a chance of losing a portion of the sample or mixing it with air from outside the tube. Apparently, this technique is not too successful since the instructions state, "if you are not sure the procedure was done correctly, relax and do it again in the same tube." To reuse the tube under these conditions could only make the sample more suspect.
Another breath-collection device is shown and described in an article entitled, "Breath Tests in Medicine" by Michael Phillips in the July 1992 issue of Scientific American. This device is highly complex and extremely large and must be mounted upon a cart, making its usefulness limited. The Phillips device employs activated carbon filters, water traps, breath traps, pumps and many complex interconnections. The size and complexity of the device limits its use to hospitals, clinics, etc.
U.S. Pat. No. 5,052,213 illustrates a device in which a recess in a slide is positionable within a housing to act first during the gas collection as a part of the flow duct for the exhalation of air and then to act as a part of the detector during a test cycle wherein the content of the recess is directed to the detector. Thus, for at least a short period of time a sample of the exhaled air is retained in the recess and is later subject to analysis. There is no provision for removing the sample from the recess for analysis by anything other than the associated device.
U.S. Pat. No. 4,617,821 shows a free standing gas detection device which includes both the collection and analysis of a breath sample in one unit. U.S. Pat. No. 5,111,827 shows a combined device which contains both a sampling connector for a gas analyzer and spirometer. U.S. Pat. No. 4,067,320, provides a drift compensation system for a gas analyzer. No effort is made to seal a sample of gas or breath in a batch device for later analysis in an independent analyzer.
Despite all of these efforts in the art, however, there have still been acute needs for improvements in breath sampling devices and methods.